1. Technical Field
The present invention relates to a shutter device provided in association with an objective lens to expose printing material to a desired quantity of light during a period of exposure but to intercept the light except during said period of exposure, and particularly to such a shutter device suitable to be used with a photoprinter which requires continuous, frequent opening and shutting of the objective lens.
2. Prior Art
The conventional shutter mechanism used with the photoprinter or the like differs from the shutter for photographic cameras in that said shutter mechanism used with photoprinters is opened and shut for each printing cycle, and, particularly in the case of the automatic printer or the like, such shutter mechanism must continuously open and shut at a high frequency. To meet such requirement, there has conventionally been provided before and behind the objective lens shutter blade means adapted to be swingably driven by an actuator such as a rotary solenoid to effect opening and shutting of the objective lens.
If said shutter blade means comprises a single blade, it might be necessitated to use a larger-diametered objective lens and, in addition, exposure for a relatively short time might result in an uneven exposure. Namely, while no problem will be confronted so far as the exposure time is relatively long, if the exposure time is shortened in order to achieve more rapid printing, a time interval for which the shutter blade is being actuated might be longer than a time interval for which the shutter blade is maintained in its fully opened position and, in consequence, there might occur a differential quantity of light transmitted through the objective lens between a location thereof at which said shutter blade begins to be opened and a location thereof at which said shutter blade is fully opened. Such phenomenon might prevent the printing material from being evenly exposed to an original picture and result in uneven distribution of the light.
To minimize such uneven distribution of the light, there has been proposed a shutter device utilizing a pair of shutter blades 1, 2 as shown by FIG. 4 of the attached drawings. These shutter blades 1, 2 are disc-like and formed on forward ends of respective levers 1a, 2a integrally therewith and these levers 1a, 2a are rotatably supported at their longitudinally middle points by shafts 1b, 2b, respectively. The levers 1a, 2a are formed at their other ends with slits 1c, 2c through which driving pins 3a, 4a loosely extend. These driving pins 3a, 4a are supported by rotary solenoids 3, 4, respectively, and swing over a predetermined angle as said rotary solenoids 3, 4 are energized, respectively.
Accordingly, said shutter blades 1, 2 swing over a predetermined angular range around the shafts 1b, 2b, respectively, as the associated rotary solenoids 3, 4 are energized. At a given part of this angular range said shutter blades overlap each other to intercept the light beams which would otherwise be transmitted through an objective lens 5.
Said rotary solenoids 3, 4 rotate in a same direction, more specifically, clockwise from respective positions as shown in FIG. 4 substantially by an angle of 90 degrees so that said shutter blade 1 swings away from the optical path of the objective lens 5 in a direction as indicated by an arrow P while said shutter blade 2 swings away from the optical path of the objective lens 5 in a direction as indicated by an arrow Q. Accordingly, during the period of opening, the objective lens 5 begins to be uncovered from its center toward its opposite side edges following the respective shutter blades 1, 2 swinging away from the center of the objective lens 5. During the period of shutting, the shutter blade 1 swings in the direction opposed to that as indicated by the arrow P while the shutter blade 2 swings in the direction opposed to that as indicated by the arrow Q so that the objective lens 5 is gradually shut from the opposite side edges toward the center thereof.
In this manner, the unevenness of light distribution is alleviated in comparison with the case of said single blade type shutter device.
However, with the conventional shutter device of double blade type as mentioned above, the number of parts increases and the structure becomes complicated, since a pair of shutter blades 1, 2 are separately driven by a pair of rotary solenoids 3, 4, respectively.
Moreover, the space available for installation of these two rotary solenoids 3, 4 prevents the photoprinter or the like from being made compact.
To alleviate the unevenness of light distribution and thereby to stabilize the operation, the pair of shutter blades 1, 2 must synchronously swing. This requirement is met only by a complicated driving circuit which necessarily leads to an increase in cost conjointly with said increased number of parts.
Additionally, it can not be assured that the rotary solenoids 3, 4 evenly operate and therefore the unevenness of light distribution can not be reliably excluded.
Synchronous operation of the pairly provided rotary solenoids 3, 4 makes a correspondingly loud sound and may be a source of undesirable noise.
In view of these problems, it is a principal object of the present invention to provide a shutter device so improved over the prior art that the mechanical structure as well as the driving circuit for the actuator can be simplified, the operation can be stabilized so as to alleviate the unevenness of light distribution more effectively and the photoprinter or the like can be made sufficiently compact.